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ModellingofSteamTurbineanditsGoverningSystem
DrMSRMurty
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GENERATORCONTROLS
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Grid
Reference
ST : steam turbineG : generator
SV : stop valve
CV
SVSteam
Speed
Power
GOVERNINGSYSTEM G
ST
CV contr. valve valve
Fig. 1 STEAM TURBINE GOVERNING SCHEME
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SPEED
+
Valve
Position
SET
POINT -
Mechanical
Power
+GOVERNOR TURBINE ROTOR
INERTIA
Fig2GOVERNINGSYSTEMFUNCTIONALBLOCKDIAGRAM
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GoverningControlsystem
SpeedSensing :Mechanical(Flyballtype),Hydraulic(Pump),Electric(toothedWheelpickup)
MWTransducerforPower Processing :Hydromechanical,Electrohydraulic,DigitalElectrohydraulic
Amplification:Hydraulicamplifiersinvariousstages
Actuation:HydraulicServomotor
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TG Unit Operating Modes:Isolated : S Open : Speed changes when gov valve is adjustedInterconnected : S Closed or grid connected: Speed is unaffected
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TGUnitOnGrid:LoadControl
TGSpeed/Frequencydoesnoteffectgridfrequency
Aftersynchronization,changeinvalveopeningcannotchangeTGunitspeedbutchangesonlyPowerOutput
InfiniteInertiaBusGRID
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ControlRequirements Startup: To control machine speed forproper synchronization
Normal Operation: To Control MW and Toparticipate in the control of system frequency
Emergency: Load Rejection/Circuit BreakerOpeningTo restore speed deviation quickly withoutmuch transient overspeed
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Governingsystem:Technology
MechanicalHydraulicControl(MHC) Electro HydraulicControl(EHC)Sensing,Processing,primaryamplificationusingelectroniccircuitry
Transistorversion(BHEL/KWUSiemensIskamaticmodules)
DigitalElectro HydraulicControl(DEHC)Microprocessorbased
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Processing
Decideshowvalvepositionshouldbechangedwhenspeedchanges
Objective:Minimumupsetsinthesystem SpeedController,LoadController:structureandtuningdecidetransientperformance
Droopcharacteristic(4%or5%):importantgoverningparameter
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ElectronicControllerFeatures
SeparationofSpeedControlandLoad(Power)Controlfunctionswithseparateprocessingphilosophy
SpeedController:Proportional Derivativeaction:AnticipatoryControl
LoadController:Proportional Integralaction InteractionwithATRS andTSE
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SimpleSpeedgoverningsystem
/Gate
Command
GateOil
ServomotorSENSING
PROCESSING AMPLIFICATIONANDACTUATION
SETPOINT
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Steam
Actuation of Valve (Servomotor)
Hydraulic Amplification
Speed & MW
PrimaryAmplification
Sensing
Processing
Electro-hydraulicConverter
ControlValve
EH
HYDRAULICPART
ST
G
ELECTRONICPART
Fig 3 ELECTRO HYDRAULIC GOVERNOR SCHEME
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VALVEOPENINGCOMMAND
Load
Speed
+
+LoadRef.
SpeedRef.
SPEEDCONTROLLER
(PDP)
LOADCONTROLLER
( P I )
SELECTIONLOGIC
(MIN MAX)
Fig 4 SPEED CONTROLLER AND LOAD CONTROLLER IN EHG
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DroopCharacteristic
SpeedChange
TurbinePowerChange
=(Load)
ValveOpeningChange
SteamFlowChange
Load%
SpeedOrFrequency
104%
100%
0 50 100
52Hz
50Hz
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Frequency(Hz)
50
524% Drop
Load0% 50% 100%
Fig 6 REGULATION OR DROOP CHARACTERSTIC
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Time (Sec)
Speed(%)
Unstable
Oscillatory (Hunting)
Fig 7 TYPICAL SPEED HUNTING TRANSIENT
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ValveOpening
Dead band or insensitive zone
Speed / frequency
Fig. 8 DEAD BAND CHARACTERISTIC
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STEAMTURBINESCHEMEWITHHPANDIPCONTROLS
Reheater
IPCV
HPCVSteam
Condenser
LPTHP
T
IPT G
R H
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TransferFunctionofSteamVolume
Steam Vessel
Steam inflow Steam
outflow
Steam pressure
1----------(1 + TV. s)
Wi W o
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Functionalblockdiagramofturbinegoverningsystem
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TURBINECONTROLLER
29Feed forward provision
KSVSSpeed Controller: Proportional Derivative
Load Controller : Proportional Integral
Load
Load Ref
SpeedRef SPEED
CONTROLLER
LOADCONTROLLER
SELECTIONLOGIC
EH
To Hyd.Amplifier
speed
Ks(1+VsTs.S)(1 + Ts . S)droop
KPL + 1TILS
KS
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PI
t
Output(Y)
t
PDP
K
Output(Y)
SpeedController LoadController
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Parametersinfluencingtheperformance
RotorInertia Droop Speed/LoadControllerparameters Deadband Valvecharacteristics IPTurbinecontrol Pressurecontrolmodes
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GovernorRegulationorDroop
4%Droop:4%SpeedChangewillcause100%changeinPowerOutput(Gain:25)
Droopisnecessaryfori)Sharingofloadii)Ensuringclosedloopstability:Lowervalueofdroopincreasesgainandmakesthesystemoscillatory
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GoverningSystemResponse
Responsetimesareimportant:delayincorrectioncancausetransientspeedrisehighandtriptheturbine
Stabilityofgoverningsystemdependsonprocessingalgorithm(PI,PID,PDPetc.,)andonsystemparameters&timeconstants
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Performancespecifications:LoadRejection
Rejectiontozeroloadfromanyload Speedshallbereturnedtothesetpointasmaybemodifiedbyspeeddrooporregulation
Nomorethanoneunderspeeddeviationexceeding5%
Nomorethanoneoverspeeddeviationexceeding5%afterinitialoverspeeddeviation
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Performancespecifications:Sustainedconditions
Steadystategoverningspeedband:Notmorethan0.3%(atnoloadoranyload).Alsocalledspeedstabilityindex.
Steadystategoverningloadband:Notmorethan0.4%(at5%speeddroop)Alsocalledpowerstabilityindex.
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StabilityIndex:Degreeofstability
Judgedbythemagnitudeofsustainedoscillationsofspeedandpoweroutputfromtheturbinethatareproducedbythegovernorsystem
Stabilityindexillustratestheregulatingperformanceforthegovernorandturbine
GovernorDeadbandillustratestheperformanceforthegovernoralone
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LoadRejection
GoverningSystemPerformancecanbejudgedbyfullloadrejectionbehavior:TransientSpeedRise(TSR),hunting
EmergencyGovernorshouldnotgetactivated Influencingparameters:RotorAccelerationTime(Ta),Droop,SpeedControllergains,Incrementaldroop
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LOADREJECTIONRESPONSE
Load
100%
Time(sec)
t
100%0%
Speed(%)
TSR(6 10%)
5%Droop
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3FW
SH1
QDRUM
WW
BOILER
SH2
G
Q
150ata540C
HTP
IPT
COND
RH
.
.
.
FlueGas
Fuel
Air
DESH
InteractionwithBoilerControls
GOVERNOR
MasterPressureControl
DrumLevelcontrol
TemperatureControl
Spray
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ExtractionSteamPressure
STEAM
CONDENSER
LPCVLOAD
SPEED
HPT
LPT
G
GOV,SYSTEM
HPCV
TO PROCESS
EXTRACTION TURBINE CONTROL SCHEME
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StreamGenerators
LP
Process
VHP HP MPPRDS
Process ProcessProcess
HRSGs
UBs
G
TypicalSteamandPowerSystem
Headers
107/ 510 45/ 400 20/ 340 5.5/ 220
Kg/Cm2 o C
C
G
GAS TURBINE
GSteam Turbine
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SteamandPowersystemDynamics
Steam System
Power System
Fuel System
Upsets in one system can influence the other
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ModellingandSimulation
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Instantaneousresponse
AssumesuddenLoadReductionandinstantaneouschangeingeneration
1.0
.8
Powerp.u Load,PL
Time(Sec.)
GenerationPg
Frequency
Time(Sec.)
50Hz
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RotorInertia
Atsteadystate:TurbineTorque(Pm)=LoadTorque((Pel)
Duringtransient:Speed=((Pm Pel)/Ta)dt
Ta=Accelerationtimeorinertiaconstant(functionofmomentofinertia)
Typicalvalues:Ta=9 12sec
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Acceleration/Deceleration
me
Pg
Deviationareaisindicativeofacceleration/deceleration
PL
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PL me
Pg
DelayduetothecumulativeeffectsofGovernor,hydraulicpassages,turbine
n or f
t
Frequency or SpeedvariationDue to the above :
GovernorResponse
SettlingSpeedhigher
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Xp
Hydraulicrelaystimeconstant
Inflow(Qi) Xp
Qi=volumetric
displacementofoil
=Ap.dxsm/dtKpXp=Apsxsm
Xsm
Xsm1
Tsm.S Xp
bLevergain
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HPTURBINETIMECONSTSANT
T4=Steammassinsideturbine
MassflowthroughHPturbineKg/Sec207.4VolumexDensity=0.844(m3)(1/0.02337) =36.114
T4=36.114/207.4=0.17Sec.
VHPincludes: Volumeininletportionupto1st stage.
allpipingconnections blading
IPTurbine:0.27Sec
LPTurbine:0.47Sec
TReheaterr :10to20Sec.
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NALCO
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NALCO
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GNFC Bharuch
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GNFC Bharuch
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GNFC Bharuch
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GNFC Bharuch
